Suppress wrong_self_convention clippy false positive

rust-lang/rust-clippy#6983

    error: methods with the following characteristics: (`to_*` and `self` type is `Copy`) usually take `self` by value
       --> src/token.rs:563:18
        |
    563 |     fn to_tokens(&self, tokens: &mut TokenStream) {
        |                  ^^^^^
        |
        = note: `-D clippy::wrong-self-convention` implied by `-D clippy::all`
        = help: consider choosing a less ambiguous name
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#wrong_self_convention

src/lib.rs

@@ -267,7 +267,9 @@
     clippy::never_loop,
     clippy::too_many_arguments,
     clippy::trivially_copy_pass_by_ref,
-    clippy::unnecessary_unwrap
+    clippy::unnecessary_unwrap,
+    // clippy bug: https://github.com/rust-lang/rust-clippy/issues/6983
+    clippy::wrong_self_convention
 )]
 // Ignored clippy_pedantic lints.
 #![allow(